Joints of Hand

Introduction

The joints of the hand are highly specialized to provide both stability and remarkable mobility, enabling precise and coordinated movements. These adaptations allow humans to perform a wide range of skilled activities such as writing, drawing, sewing, handling surgical instruments, using tools, and manipulating small objects with great accuracy.

The articulations of the hand are classified into the following groups:

1. Intercarpal joints – Joints between adjacent carpal bones.
2. Midcarpal joint – Joint between the proximal and distal rows of carpal bones.
3. Carpometacarpal joints – Joints between the distal row of carpal bones and the bases of the metacarpals.
4. Intermetacarpal joints – Joints between the bases of adjacent metacarpal bones.
5. Metacarpophalangeal (MCP) joints – Joints between the heads of the metacarpals and the bases of the proximal phalanges.
6. Interphalangeal (IP) joints – Joints between adjacent phalanges of the fingers and thumb.

Intercarpal joints

The intercarpal joints are the articulations between adjacent carpal bones. These joints contribute to the flexibility and stability of the wrist.

Arrangement of the Carpal Bones

The eight carpal bones are arranged in two rows.

Proximal row

• Scaphoid
• Lunate
• Triquetrum
• Pisiform

Distal row

• Trapezium
• Trapezoid
• Capitate
• Hamate

Type

• The intercarpal joints are plane synovial joints.

Pisiotriquetral joint

The pisotriquetral joint is formed between the pisiform and the triquetrum.

Type

• Plane synovial joint

Midcarpal joint

The midcarpal joint is situated between the proximal and distal rows of the carpal bones.

Type

• Compound ellipsoid synovial joint

Articular Surfaces

• Formed between the distal surfaces of the scaphoid, lunate, and triquetrum (pisiform excluded) and the proximal surfaces of the trapezium, trapezoid, capitate, and hamate.

Carpometacarpal joints

The carpometacarpal joints are formed between the distal row of carpal bones and the bases of the metacarpals.

Type

• Second to fifth CMC joints: Plane synovial joints
• First CMC joint (thumb): Saddle synovial joint

Intermetacarpal joints

The intermetacarpal joints are formed between the adjacent bases of the second to fifth metacarpals.

Type

• Plane synovial joints

First Carpometacarpal Joint

The first carpometacarpal joint is the articulation between the trapezium and the base of the first metacarpal. It is the most mobile carpometacarpal joint and is responsible for the remarkable mobility of the thumb.

Type

• Saddle (sellar) variety of synovial joint

The unique saddle-shaped articular surfaces allow movement in two planes as well as axial rotation, making the thumb highly versatile.

Articular surface

Proximal Articular Surface

• Inferior surface of the trapezium

Distal Articular Surface

• Superior surface of the base of the first metacarpal

Both articular surfaces are reciprocally concavoconvex, with each surface being concave in one direction and convex in the other. This reciprocal arrangement is characteristic of a saddle joint and permits a wide range of movements.

Ligaments

Capsular Ligament

• A strong fibrous capsule surrounds the joint.
• Attached to the margins of the articular surfaces of the trapezium and first metacarpal.
• The inner surface is lined by the synovial membrane.

Lateral Ligament

• A broad ligament extending from the lateral surface of the trapezium to the lateral aspect of the base of the first metacarpal.
• Reinforces the lateral side of the joint.

Anterior and Posterior Ligaments

• Oblique fibrous bands extending from the anterior and posterior surfaces of the trapezium to the medial side of the base of the first metacarpal.
• These ligaments strengthen the anterior and posterior aspects of the joint.

Relations

Anterior

• Muscles of the thenar eminence

Posterior

• Tendons of:
  • Extensor pollicis longus (EPL)
  • Extensor pollicis brevis (EPB)

Medial

• Radial artery
• First dorsal interosseous muscle

Lateral

• Tendon of abductor pollicis longus (APL)

Blood and Nerve Supply

Blood Supply

• Supplied mainly by branches of the radial artery.

Nerve Supply

• Articular branches arise primarily from the median nerve.

Movements

The first carpometacarpal joint permits movements in multiple planes because of its saddle-shaped configuration.

The first metacarpal is positioned anteriorly and rotated medially by approximately 90° relative to the other metacarpals. Consequently, movements of the thumb occur at right angles to those of the fingers.

Flexion

• Movement of the thumb across the plane of the palm toward the little finger.

Extension

• Movement of the thumb away from the palm in the plane of the palm.

Abduction

• Movement of the thumb away from the palm in a plane perpendicular to the plane of the palm.

Adduction

• Movement of the thumb back toward the plane of the palm from the abducted position.

Opposition

• A complex movement in which the thumb is brought across the palm so that the pulp of the thumb contacts the pulp of one or more fingers.
• This movement combines abduction, flexion, and medial rotation of the first metacarpal.
• Opposition is the anatomical basis of the human hand’s precision grip and fine manual dexterity.

Circumduction

• A circular movement produced by the sequential combination of flexion, extension, abduction, and adduction.

Table 15.1: Movements of thumb and responsible muscle

Movement	Principal Muscles
Flexion	Flexor pollicis longus, Flexor pollicis brevis, Opponens pollicis
Extension	Extensor pollicis longus, Extensor pollicis brevis
Adduction	Adductor pollicis
Abduction	Abductor pollicis longus, Abductor pollicis brevis
Opposition	Opponens pollicis (chief muscle)

Metacarpophalangeal Joints

The metacarpophalangeal (MCP) joints are formed by the articulation of the heads of the metacarpal bones with the bases of the proximal phalanges. These joints provide both stability and mobility, allowing the fingers to perform powerful grasping as well as fine, precise movements.

Type

• Ellipsoid (condyloid) variety of synovial joints

Being biaxial joints, they permit movement in two planes.

Articular Surfaces

Proximal (Superior) Articular Surface

• Rounded head of the metacarpal

Distal (Inferior) Articular Surface

• Shallow base of the proximal phalanx

The convex metacarpal head articulates with the concave base of the proximal phalanx.

Ligaments

Capsular Ligament

• A fibrous capsule surrounds each metacarpophalangeal joint.
• It is attached to the margins of the articular surfaces and lined internally by a synovial membrane.

Palmar (Volar) Ligament

• A strong fibrocartilaginous plate firmly attached to the base of the proximal phalanx.
• Reinforces the palmar aspect of the joint.
• Prevents hyperextension and increases joint stability.

Collateral Ligaments

Each joint is strengthened on either side by:

• Medial collateral ligament
• Lateral collateral ligament

These are strong, cord-like fibrous bands that stabilize the joint during flexion and gripping.

Movements

The metacarpophalangeal joints permit the following movements:

• Flexion
• Extension
• Abduction
• Adduction
• Circumduction

Table 15.2: Movements at metacarpophalangeal (MP) joint and responsible muscles

Movement	1st MP joint	2nd–5th MP joints
Flexion	Flexor pollicis longus Flexor pollicis brevis	Interossei Lumbricals
Extension	Extensor pollicis longus Extensor pollicis brevis	Extensors of fingers
Adduction	Adductor pollicis	Palmar interossei
Abduction	Abductor pollicis	Dorsal interossei

Interphalangeal Joints

The interphalangeal (IP) joints are the articulations between adjacent phalanges of the digits.

• The index, middle, ring, and little fingers each have:
  • Proximal interphalangeal (PIP) joint
  • Distal interphalangeal (DIP) joint
• The thumb has only one interphalangeal (IP) joint between its proximal and distal phalanges.

Type

• Hinge variety of synovial joints

These are uniaxial joints that permit movement in a single plane.

Ligaments

Each interphalangeal joint is reinforced by:

• Fibrous capsule
• Palmar (volar) fibrocartilaginous ligament (volar plate)
• Medial collateral ligament
• Lateral collateral ligament

These structures provide stability while preventing excessive lateral movement and hyperextension.

Movements

As hinge joints, the interphalangeal joints permit only:

• Flexion
• Extension

Muscles Producing the Movements

Table 15.3: Movements of interphalangeal joints and responsible Muscles

Movement	Thumb (IP Joint)	Index to Little Fingers
Flexion	Flexor pollicis longus	Proximal IP (PIP): Flexor digitorum superficialis and Flexor digitorum profundus Distal IP (DIP): Flexor digitorum profundus
Extension	Extensor pollicis longus	Extensor digitorum, assisted by the lumbricals and interossei

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